The use of reclaimed asphalt pavement (RAP) as a base layer is gaining popularity, but there are gaps in the literature about its material performance. One problem not well investigated is the variability in the resilient modulus (MR) of RAP as a base layer, as compared with typical granular material, and the impact of this variability on pavement performance. Selection of one MR value has its own variability, beyond the expected variability in the base layer R that results from the use of aggregates with different qualities. This paper investigates the effect of three sources of variability to determine the base layer resilient modulus in the laboratory for RAP as compared with granular material. The three sources considered were (a) the variability in the material and sample preparation for the MR testing, (b) the constitutive model used to predict the resilient modulus, and (c) the state of stress used to predict the base layer modulus. The study compared the variability of the MR of RAP with the MR of unbound granular materials on the basis of actual test results. The impact of MR variability on the flexible pavement distresses for RAP as compared with granular material was investigated using the Mechanistic-Empirical Pavement Design Guide.